1. Field of the Invention
This invention pertains to the field of polymer resins, curable thermoset resins, resin systems which include curable thermoset resins, composite materials and skin laminates for composite materials, and processes and intermediates for making the same.
2. Description of Related Art
Known gel coated fiber-reinforced polymers are subject to blistering if immersed in water or solvents for a prolonged period of time unless special measures are taken to prevent this phenomenon. Blisters are raised by localized swelling of the gel coated laminate due to diffusion of water into the composite and the presence of water-soluble constituents within the laminate. The blisters not only effect the external appearance of the gel coated fiber-reinforced polymer article, but also eventually lead to reduced composite strength.
Several methods have been proposed to reduce blistering in gel coated composite materials. U.S. Pat. No. 4,724,173 describes using a permeable gel coat to allow the osmotically active molecules to diffuse from the osmotic centers through the gel coat at a defined transport rate whereby the osmotic pressure of the osmotic centers is reduced so as to reduce blistering. U.S. Pat. No. 4,477,325 describes a method of manufacturing a skin barrier which has improved water resistance to protect the composite material from hydrolysis. U.S. Pat. Nos. 4,480,077 and 4,525,544 describe vinyl ester resin compositions which may be used in the laminate construction to impart greater resistance to water permeation and U.S. Pat. No. 4,959,259 describes a bisphenolic polyester resin composition which may also be used to impart greater water permeation resistance.
The latter technique, using a laminate resin having greater corrosion and/or water resistance, is the most common technique used by the composite industry to reduce blistering. Those resins are typically vinyl ester resins or isophthalic polyester resins. Not only is that technique not always completely successful, it also increases the overall expense of the composite material and/or reduces the flexibility in choosing the laminating resin for other desired properties.
For these and other reasons, further improvements in the ability to prevent blistering are desired. These improvements have special significance in outdoor and marine applications, bathtubs and shower stalls and environments exposed to chemicals, such as industrial and commercial applications. These and other objectives are achieved by the present invention.